95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
//
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// use_future.hpp
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// ~~~~~~~~~~~~~~
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//
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// Copyright (c) 2003-2016 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#ifndef BOOST_ASIO_USE_FUTURE_HPP
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#define BOOST_ASIO_USE_FUTURE_HPP
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#if defined(_MSC_VER) && (_MSC_VER >= 1200)
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# pragma once
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#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)
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#include <boost/asio/detail/config.hpp>
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#include <memory>
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#include <boost/asio/detail/push_options.hpp>
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namespace boost {
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namespace asio {
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/// Class used to specify that an asynchronous operation should return a future.
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/**
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* The use_future_t class is used to indicate that an asynchronous operation
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* should return a std::future object. A use_future_t object may be passed as a
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* handler to an asynchronous operation, typically using the special value @c
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* boost::asio::use_future. For example:
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*
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* @code std::future<std::size_t> my_future
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* = my_socket.async_read_some(my_buffer, boost::asio::use_future); @endcode
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*
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* The initiating function (async_read_some in the above example) returns a
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* future that will receive the result of the operation. If the operation
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* completes with an error_code indicating failure, it is converted into a
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* system_error and passed back to the caller via the future.
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*/
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template <typename Allocator = std::allocator<void> >
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class use_future_t
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{
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public:
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/// The allocator type. The allocator is used when constructing the
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/// @c std::promise object for a given asynchronous operation.
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typedef Allocator allocator_type;
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/// Construct using default-constructed allocator.
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BOOST_ASIO_CONSTEXPR use_future_t()
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{
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}
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/// Construct using specified allocator.
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explicit use_future_t(const Allocator& allocator)
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: allocator_(allocator)
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{
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}
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/// Specify an alternate allocator.
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template <typename OtherAllocator>
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use_future_t<OtherAllocator> operator[](const OtherAllocator& allocator) const
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{
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return use_future_t<OtherAllocator>(allocator);
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}
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/// Obtain allocator.
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allocator_type get_allocator() const
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{
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return allocator_;
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}
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private:
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Allocator allocator_;
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};
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/// A special value, similar to std::nothrow.
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/**
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* See the documentation for boost::asio::use_future_t for a usage example.
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*/
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#if defined(BOOST_ASIO_HAS_CONSTEXPR) || defined(GENERATING_DOCUMENTATION)
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constexpr use_future_t<> use_future;
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#elif defined(BOOST_ASIO_MSVC)
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__declspec(selectany) use_future_t<> use_future;
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#endif
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} // namespace asio
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} // namespace boost
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#include <boost/asio/detail/pop_options.hpp>
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#include <boost/asio/impl/use_future.hpp>
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#endif // BOOST_ASIO_USE_FUTURE_HPP
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